This project is directed towards understanding the role of the prefrontal cortex (PFC) in modulating category representations in posterior visual association cortex (VAC). The causal effect of PFC modulation on these regions will be tested in patients with focal PFC damage and healthy subjects who have undergone transcranial magnetic stimulation (TMS) of a unilateral PFC region. The ability of these groups to perform a selective attention task that engages category-specific regions of cortex as well as the corresponding pattern of functional magnetic resonance imaging (fMRI) data will provide information about how this top-down modulation occurs. The task used here is designed to segregate the hemispheric responses according to the visual field of presentation. Multiple measures of category selectivity will be applied to the data to assess the hypothesized decrease in selectivity in VAC in the same hemisphere as the PFC impairment. Further, a multivariate analysis of the fMRI data obtained in the two previously described proposed experiments will identify changes in connectivity between the impaired and intact hemispheres. PUBLIC HEALTH RELEVANCE: Basic knowledge about the coupling between PFC and visual cortex gained from this work may be of fundamental clinical significance. A large number of disorders are associated, at least in part, with dysfunction of the frontal lobes. These include psychiatric disorders, such as schizophrenia, attention-deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder, and major depression, as well as a number of structural and degenerative brain diseases including Parkinson's Disease (PD)and Alzheimer's Disease (AD). Knowledge of the role of PFC in top-down modulation may guide development of directed assessments that can refine diagnosis and treatment.